Mazda 6 2.2 disel white smoke problem

Sometimes when idling, white smoke comes out of the exhaust pipe and the engine runs unevenly, this happens when I’m standing at a traffic light, and there’s a smell of diesel fuel. It may not happen for a couple of days, but then 2-3 times when I stop at a traffic light, white smoke comes out, I switch from drive to parking, the smoke stops, I start driving, and the smoke also stops. The revs don’t jump